Re: st: Problem with stset and sttocc

[Andrew Hall <A.Hall04@westminster.ac.uk>]

Dear Isabel

Please ignore my most recent message: I misunderstood the output, and 
it does not work.  Creating a new time variable does not do the 
trick.  Sorry to mess you around.

I tried creating new time variables that were different for failures 
and non-failures so that:
        failure time < non-failure time (this selected all controls 
from failures)
        failure time > non-failure time (this selected 227 controls 
from failures)
        failure time = non-failure time (this selected 221 controls 
from failures)

So I am no further forward.  I hope very much that you can help

Regards, Andrew
At 15:25 23/10/2007, you wrote:

> If Andrew could send me (privately) a dataset and a short do-file to
> replicate the problem, I would be happy to look into it.
>
>     -- Isabel
>     -- icanette(at)stata(dot)com
>
>
>
> Andrew Hall wrote:
> > Hello
> >
> > I am having problems using stset and sttocc to create a case-control
> > data set from a simple cross-sectional data set.  Sttocc is selecting
> > cases as controls.   I am using Intercooled STATA 9.2 on Windows XP.
> > This is what is happening.
> >
> > I have cross-sectional survey data on 7,572 Ethiopian schoolchildren of
> > whom 1,283 are orphans and 6,289 are non-orphans.  The variable orphan
> > is coded as 1 = orphan, 0 = non orphan.
> >
> > The data were collected between 28/11/2006 and 8/2/2007.
> >
> > I want to randomly select a non-orphan for each orphan matched on sex
> > and age at least to create a case-control data set.
> >
> > I have stset the dataset using either date of visit (dov1) as the time
> > variable or created a new time variable fixed on one arbitrary date e.g.
> > 01/01/2007 (dovfixed)
> >
> >                stset  dov1, failure(orphan=1)
> >   or          stset dovfixed, failure(orphan=1)
> >
> > This creates new temporary variables including _d which cross-tabs
> > perfectly with orphan (_d = 1 and orphan = 1 n=1283, _d =0 and orphan =
> > 0, n=6289).  It seems that the dataset have been properly stset (or has
> > it?).
> >
> > I then use sttocc to match each case to one control on the variables sex
> > (1=male; 2=female) and ageyrs (in years) as follows:
> >
> >             sttocc, match (sex ageyrs) number(1)
> >
> > This works and cannot find controls for 2 cases only.
> >
> > But when I do a cross-tab of orphan  by _case I find that 278 controls
> > who should be non-orphans have been selected from the cases (orphans,
> > failure=1).  All controls should be selected from the non-orphans.
> >
> > Snapspan has no effect on the dataset as all id numbers in the data set
> > are unique anyway.
> >
> > Why are orphans (failure) being selected as controls for orphans
> > (failure) when I have specified non-orphans? Am I just being dim?  Is
> > there something wrong the way I'm using stset?  I have tried setting
> > origin, enter and exit, but they are not really relevant as all subjects
> > were in effect studied on the same day, so it is not time  series data.
> > I am something of a novice and can't find any similar issues discussed
> > on the listserv archives, hence my request..
> >
> > Thanks for reading this and suggestions would be gratefully received.
> >
> >
> > Andrew Hall MSc PhD RPHNutr
> >
> > Reader in Public Health Nutrition
> > Centre for Public Health Nutrition
> > Westminster University
> > 115 New Cavendish Street
> > London W1W 6UW
> >
> > Tel: + 44 (0)207 911 5000 Ext 3910
> >
>
>
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